THE LIFE-HISTORY OF FRESH- WATER MITES. 361 



Fig. 1, d, is copied from Van Beneden to show how the eggs of 

 Atax ypsilophorus are deposited on the branchiae of the fresh- 

 water mussel. Mr. Williamson, of Edinburgh, has known species 

 of the genus Lebertia to deposit eggs in the water, and says that 

 they were pear-shaped, and in twos and threes, without the 

 gelatinous envelope we find covering the eggs of other water- 

 mites. It may be that some of the mites will only deposit eggs 

 when the position is favourable for the parasitic stage. For 

 instance, I kept a number of females of Atax ijpsilophorus which 

 were all filled with eggs for quite a long time in a small tank, but 

 no eggs were deposited. 



I have been able to watch the incubation period of several 

 different species of water-mites. Take, for example, Fiona longi- 

 palpis, Kren. This is one of the finest species of the genus, and 

 allows observations to be taken very easily on account of its size. 

 Plate 26, Fig. a, is a sprig of Anacharis. At Fig. b is shown how 

 the eggs were placed on the upper-side of the leaf, always in a row, 

 but not always of the same number. Fig. c is a side view showing 

 the depth, and demonstrating how each egg is enveloped in 

 a gelatinous film. The eggs seem to be laid separately, for 

 the line of demarcation in the protective film is plainly seen for 

 some considerable time after oviposition, this division graduallv 

 disappearing as the eggs develop. These eggs were deposited 

 on April 28th, 1904. The drawing, Fig. d, was made on 

 May 2nd, and after that every second day, until the living larvae 

 escaped through the slits shown in Fig. Jc, which occurred on 

 May 15th. It will be seen on reference to the Figs, d — I that 

 the egg gradually grew during that time, and assumed the 

 peculiar form of the larva. Fig. m is the dorsal surface of 

 a larval form just hatched, and Fig. n is a larger drawing 

 of the same, showing the ventral surface. All the larval 

 forms have only six legs, and are, for the time being, free 

 swimmers. They vary greatly in form — so much so that, 

 in the extreme cases, Atax, Neumania, llj/grobates, Limnesia . 

 Hi/drachna, Diplodontus, and Arrhenurus, we can tell almost 

 certainly to which genus any larval form belongs. But when it 

 is a question as to the specific identity of the larva the case 

 is very different — the differences between the species in the 

 larval stage being so small. It is supposed that, as soon as the 

 larva has escaped from the egg, its first duty is to look for 



